Assessment of coupled irregularity effects on seismic performance of buildings on hill slopes

In this study, the seismic performance of buildings with coupled irregularities is investigated – both in plan and elevation; such buildings are common in hilly terrains. A field survey is conducted using rapid visual screening to investigate prevalent building configurations in hilly regions, with an emphasis on Srinagar Garhwal, Pauri town and Rudraprayag city located in the state of Uttarakhand, India. In total, 1558 structures exhibiting plan and/or vertical irregularities are documented, influenced by the underlying slope gradient. Based on the identified configurations, 12 building models incorporating re-entrant corners, non-parallel lateral force systems, step-back and split foundations are developed in finite-element-based software. Non-linear time history analysis is performed using a suite of 11 ground motions. Key structural parameters, including the fundamental period, torsional irregularity, interstorey drift, peak roof displacement and peak floor acceleration, are evaluated. The results highlight that buildings with coupled irregularities experience significantly amplified seismic demands in contrast to the regular models. The study also investigates the influence of seismic incidence angle, identifying 135° as the most critical. Unlike prior studies, this work addresses a critical gap in code-based design practices and provides valuable recommendations for seismic design guidelines, emphasising the need for irregularity-sensitive detailing in hillside construction.